ABSTRACT
Summary Introduction: Due to the mandatory use of a mask in the context of the COVID-19 pandemic, and the authorization to do outdoor sports in Catalonia, we set out to evaluate the physiological impact of the hypoxia and hypercapnia generated by the mask during aerobic exercise. Methods: 46 adolescent competitive athletes (35 women, 11 men) were evaluated. Measurements were taken of ambient air, at rest intra-mask, and during a stress test intra-mask. The concentration of O2 and CO2 intra-mask and the O2 Saturation were evaluated. Results: The O2 of ambient air in the laboratory: 20.9%;Basal intra-mask O2: 18.0 ± 0.7% and intra-mask O2 during exercise: 17.4 ± 0.6% (p <0.0001). The CO2 was: 0.05 ± 0.01% environmental;baseline intra-mask: 1.31 ± 0.5%, and during exercise intra-mask: 1.76 ± 0.6% (p <0.0001). Baseline O2 saturation with mask was 98.4 ± 0.6% and immediately after exercise was 97.1 ± 2.8% (p <0.03). During the exercise intra-mask, 30% of the young athletes exceeded 2% of CO2 and 22% breathed oxygen with a concentration lower than 17%. Conclusions: The use of masks generate hypercapnic hypoxia during exercise. One third of the subjects exceed the CO2 threshold of 2%.